1. Field of the Invention
Embodiments of the invention generally relate to catwalks for conveying pipe to a drill floor from a lower section of a drilling rig or drill site. Specifically, embodiments of the invention relate to an emergency cylinder lowering circuit which allows the catwalk trough to be lowered remotely to its home position in a safe manner in the event of a hydraulic failure.
2. Description of the Related Art
In a drilling operation or rig work-over operation, whether on a water-based or land-based drilling rig, pipe for the drilling operation, casing, or other tubulars are often stored at or supplied from a level that is lower than the drill floor. Operators typically use a “catwalk” to convey the pipe from the lower level to the drill floor. The pipe is typically mechanically transported (e.g. pushed by a skate and/or pulled in catwalk in a v-shaped trough) from a level below the rig floor to the rig floor.
In prior art catwalks, the trough is raised using hydraulic cylinders which raise a leg of the catwalk. Prior art hydraulic cylinders used with catwalks have counter balance valves, one on each end of the cylinder, that maintain pressure within the cylinder in the event that a hose breaks or the hydraulic power unit (HPU) fails. As a result, the counter balance valves prevent the cylinders, and the catwalk, from moving up or down. In order to lower the catwalk, current systems require the counter balance valves to be manually opened so that the hydraulic fluid can flow to the rod end and the tank and the hydraulic cylinders can retract to their home position.
Accordingly, it would be useful to have a system that allows catwalk users to control the routing of hydraulic fluid from a remote location so that the catwalk can be slowly and safely returned to its home position.